Significant Accounting Policy Earnings Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Dec. 31, 2015	Jun. 30, 2015	Mar. 31, 2015	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items]
Income (Loss) from Continuing Operations, Including Portion Attributable to Noncontrolling Interest									$ (535,965)	$ (350,266)	$ 164,947
Income (Loss) from Continuing Operations Attributable to Parent	$ (321,198)	$ 62,568	$ 45,342	$ (234,044)	$ (43,291)	$ 129,312	$ (577,884)	$ 52,964	(544,919)	(360,676)	164,947
Discontinued Operation, Income (Loss) from Discontinued Operation During Phase-out Period, Net of Tax	19,564	(34,975)	(11,017)	(234,605)	(53,167)	(3,842)	(25,417)	26,067	(303,183)	(14,209)	(1,857)
Less: Net Loss (Income) Attributable to Noncontrolling Interest									(8,954)	(10,410)	0
Net Income Attributable to CONSOL Energy Inc Shareholders	$ (306,047)	$ 25,345	$ 30,405	$ (469,828)	$ (97,572)	$ 118,980	$ (603,301)	$ 79,031	$ (848,102)	$ (374,885)	$ 163,090
Weighted Average Number of Shares Outstanding, Basic									229,387,403	229,186,125	229,994,407
Effect of stock-based compensation awards									0	0	1,585,871
Weighted Average Number of Shares Outstanding, Diluted									229,387,403	229,186,125	231,580,278
Earnings Per Share, Basic	$ (1.33)	$ 0.11	$ 0.13	$ (2.05)	$ (0.43)	$ 0.52	$ (2.64)	$ 0.34	$ (3.70)	$ (1.64)	$ 0.71
Income (Loss) from Discontinued Operations and Disposal of Discontinued Operations, Net of Tax, Per Basic Share	0.09	(0.15)	(0.05)	(1.02)	(0.24)	(0.02)	(0.12)	0.11	(1.32)	(0.07)	(0.01)
Income (Loss) from Continuing Operations, Per Basic Share	(1.42)	0.26	0.18	(1.03)	(0.19)	0.54	(2.52)	0.23	(2.38)	(1.57)	0.72
Earnings Per Share, Diluted	(1.33)	0.11	0.13	(2.05)	(0.43)	0.52	(2.64)	0.34	(3.70)	(1.64)	0.70
Income (Loss) from Discontinued Operations and Disposal of Discontinued Operations, Net of Tax, Per Diluted Share	0.09	(0.15)	(0.05)	(1.02)	(0.24)	(0.02)	(0.12)	0.11	(1.32)	(0.07)	(0.01)
Income (Loss) from Continuing Operations, Per Diluted Share	$ (1.42)	$ 0.26	$ 0.18	$ (1.03)	$ (0.19)	$ 0.54	$ (2.52)	$ 0.23	$ (2.38)	$ (1.57)	$ 0.71